Metal hydroxides or bases . A hydroxide or a base is the result of the combination of a metal oxide (basic oxide) with water.
Basic Oxide + H2O ———> Hydroxide
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- 1 Concept
- 2 Features
- 3 Properties
- 4 Chemical nomenclature and notation
- 5 Obtaining
- 6 Applications
- 7 See also
- 8 Sources
Metal hydroxides are ternary compounds (that is, made up of three elements): a metal, oxygen and hydrogen In metal hydroxides, oxygen and hydrogen are formed by one or more OH groups (hydroxyl groups), so these compounds always they have the same number of oxygen atoms as hydrogen.
Metal hydroxides are made up of OH- ions and metal cations. Example:
- Sodium hydroxide , NaOH, which is commonly known as caustic soda .
- Potassium hydroxide , KOH, caustic potash.
- Calcium hydroxide , Ca (OH) 2, slaked lime or lime water, widely used in medicine.
- Aluminum hydroxide , Al (OH) 3, a fundamental component of alusil .
- Magnesium hydroxide , Mg (OH) 2, magnesium magma .
- Iron hydroxide II , Fe (OH) 2, ferrous hydroxide .
- Iron hydroxide III , Fe (OH) 3, ferric hydroxide .
- The hydroxyl ion or radical (OH-) characterizes them.
- They have a bleach flavor (bitter like soap).
- They are slippery to the touch.
- With the methyl orange indicator, a yellow color appears, phenolphthalein shows a deep red color and with litmus it turns blue.
- They are generally corrosive.
- They have detergent and soapy properties.
- They dissolve oils and sulfur.
- They react with acids to produce salts.
- Metal hydroxides are solid substances at room temperature.
- The hydroxides of the elements of group IA of the periodic table melt at relatively high temperatures. Most of the remaining metal hydroxides decompose at high temperatures before melting.
- Taking into account their solubility in water, metal hydroxides are classified as soluble and practically insoluble.
- The chemical elements of group IA (alkaline) and some of the elements of group IIA (alkaline-earth) of the periodic table form soluble hydroxides, the rest are not.
- Solid state metal hydroxides do not conduct electric current and they do so in molten or aqueous solution.
Chemical nomenclature and notation
To write the chemical formula or to name the metal hydroxides, the same procedures are used as for the oxides , bearing in mind that the polyatomic group is always the hydroxide.
To name metallic hydroxides, the word hydroxide is placed, followed by the preposition of and then the name of the metallic element , indicating with a Roman number the oxidation number if it is variable.
To represent the chemical formula of a metal hydroxide known by its name, the following steps can be followed:
The obtaining of the hydroxides varies from some hydroxides to others. Those generally used in the cases indicated are the following:
- Electrolysis of the chloride of the corresponding element in aqueous solution. It is applied to alkaline hydroxides. It has great industrial importance in the case of NaOH -mainly- and KOH.
- By reaction of the corresponding oxide with water: It is applied to the alkaline earth hydroxides: calcium, strontium and barium. It is widely used to obtain the product used in construction, called slaked lime.
- By precipitation of salts of the corresponding element with alkali hydroxides or ammonia: It is used in the case of very poorly soluble hydroxides.
Metal hydroxides have great application in industry, life and the laboratory.
- The property of alkalis to react with proteins is used in the determination of the percentage of wool in the tissues.
- Other hydroxides are used in medicine when the presence of a basic medium in the body is needed to combat heartburn. For example, aluminum hydroxide.
- Calcium hydroxide is used in the sugar industry to control the acidity of the guarapo and in agriculture to vary the degree of acidity of the soils, it is also used in construction, to join bricks and blocks and to repel walls and is used in dentistry to repair damaged dentures.
- The solution of barium hydroxide (barite water) and calcium hydroxide (lime water) are used for the identification of carbon dioxide .
- Calcium hydroxide suspension (lime milk) is used as a paint and in the chemical industry.
- Soda and caustic potash are used in the manufacture of soaps.
- Iron hydroxides (limonites), in addition to being ores of this metal, are used in the preparation of paints to protect iron and wood. As it has great surface adsorption, it is used for water purification and for the removal of hydrogen sulphide gases from the air.
- Sodium hydroxide is used in the manufacture of paper, soaps, textile fibers, etc.